diff --git a/test/groovy/util/JenkinsWriteFileRule.groovy b/test/groovy/util/JenkinsWriteFileRule.groovy
index 6a59dcf32..5c48b2748 100644
--- a/test/groovy/util/JenkinsWriteFileRule.groovy
+++ b/test/groovy/util/JenkinsWriteFileRule.groovy
@@ -1,6 +1,9 @@
 package util
 
 import com.lesfurets.jenkins.unit.BasePipelineTest
+
+import static org.junit.Assert.assertNotNull
+import static org.junit.Assert.assertTrue
 import org.junit.rules.TestRule
 import org.junit.runner.Description
 import org.junit.runners.model.Statement
@@ -25,7 +28,17 @@ class JenkinsWriteFileRule implements TestRule {
             @Override
             void evaluate() throws Throwable {
 
-                testInstance.helper.registerAllowedMethod( 'writeFile', [Map.class], {m -> files[m.file] = m.text.toString()})
+                testInstance.helper.registerAllowedMethod( 'writeFile', [Map.class], { m ->
+                    assertNotNull(m.file)
+                    assertTrue(m.file instanceof CharSequence)
+                    assertNotNull(m.text)
+                    assertTrue(m.text instanceof CharSequence)
+                    if (m.encoding) {
+                        assertTrue(m.encoding instanceof CharSequence)
+                        // Would be nice to actually handle encoding
+                    }
+                    files[m.file] = m.text
+                })
 
                 base.evaluate()
             }
diff --git a/vars/debugReportArchive.groovy b/vars/debugReportArchive.groovy
index ebb0d153b..68de7d39c 100644
--- a/vars/debugReportArchive.groovy
+++ b/vars/debugReportArchive.groovy
@@ -63,7 +63,7 @@ void call(Map parameters = [:]) {
             echo result.contents
         }
 
-        script.writeFile file: result.fileName, text: result
+        script.writeFile file: result.fileName, text: result.contents
         script.archiveArtifacts artifacts: result.fileName
         echo "Successfully archived debug report as '${result.fileName}'"
     } catch (Exception e) {